The goal of this project is to identify maternal humoral immune responses that may prevent materno fetal HIV transmission. Our studies will initially focus on maternal antibodies to the Principal Neutralizing Domain (PND) of the gp120 envelope glycoprotein of the HTLV-III MN strain. We will, however, also investigate other neutralizing epitopes to gp120-MN-PND will be measured in the sera of materno-fetal pairs, in amniotic fluid and in body secretion (secretory IgA). IgG subclass antibodies to gp120-MN-PND will also be evaluated in maternal blood, amniotic fluid and cord bloods. Purified high affinity antibodies will be assessed in vitro for their virus neutralization capacity. The presence of these antibodies will also be correlated with maternal virus load and with fetal outcome.